Ecology of Individuals and Populations · 2020. 1. 26. · Human Population Growth •K-selected...

1

Ecology of Individuals

and PopulationsChapter 55

Environmental Challenge

• Ecology

– Study of how organisms relate to one

another and to their environments

• Key elements of the environment

– Temperature

– Water

– Sunlight

– Soil

2


• Homeostasis

– Individual must maintain a

steady-state internal

environment regardless of

external environment

• Some are “conformers” –adopt temperature, salinity

of their surroundings

3


• Reponses can be short or long term

• Short term

– From a few minutes, to an individual’s

lifetime

– Variety of ways to cope

• Long term

– Natural selection can operate to make

a population better adapted to the

environment4


• Coping mechanisms

– Physiological responses

– Morphological capabilities

– Behavioral responses

5

6

Morphological and Behavioral

Adaptations


winter

summer

wolf

polar bear

Thickness of Fur (mm)

6.05.04.03.02.01.0

1.5

Ins

ula

tio

n (°C

cal/

m2/h

)

1.0

0.5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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30

28

24

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24 26 28 30 32

Air Temperature (°C)

open habitat

shaded forest

Bo

dy

Tem

pera

ture

(°C

)



• Natural selection leads to evolutionary adaptation to environmental conditions

7

Populations

• Populations

– Groups of individuals of the same species

in one place

• 3 characteristics of population ecology

– Population range, area throughout which a

population occurs

– Pattern of spacing of individuals

– How population changes in size through

time

8

Populations

• Range

– Most species have limited geographic range

• Devil’s hole pupfish lives in a single spring in southern Nevada

– Polar bears are well adapted for the Arctic but you won’t find them in the tropics

9

Populations

• Ranges change through time

– Environment changes

– Circumvent inhospitable habitat to

colonize suitable, previously

unoccupied areas

– Humans have expanded ranges of

coyotes, introduced starlings

10

Populations

• Dispersal

mechanisms

11


Solanum dulcamara

Juniperus chinensis

Rubus fruticosus

Asclepias syriaca

Acer saccharum

Ranunculus muricatus

Bidens frondosa

Medicago polycarpa

Fleshy

Fruits

Windblown

Fruits

Adherent

Fruits

Terminalia

calamansanai

Populations

• Individuals in populations exhibit

different spacing patterns

– Random spacing

– Uniform spacing

– Clumped spacing

12

Population Demography

• Demography

– Quantitative study of populations

– How size changes through time

• Whole population: increasing,

decreasing, remaining constant

• Population broken down into parts

–Study birth and death rates of a

specific age

13

Demography and Dynamics

• Population growth can be influenced by the population’s sex ratio

– Number of births directly related to number of females

• Generation times: average interval between birth of an individual and birth of its offspring

– Populations with short generations can

increase in size more quickly than

populations with long generations

14

In general, larger organisms have longer

generation times.

15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.1 µ

m

Beaver

Body Size (length)

1 hour

1 day

1 week

1 month

1 year

10 years

100 years

10 µ

m

100 µ

m

1 m

m

1 c

m

10 c

m

1 m

10 m

100

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Sequoia

Fir

Kelp

Whale

BirchHuman

Horseshoe crab

Turtle

Clam

SpirochaetaEuglena

Pseudomonas

E. coli

Tetrahymena

DidiniumParamecium

Daphnia

Stentor

SalamanderMouse

BeeHousefly

Drosophila

Fox

Rhino

Dogwood

Elephant Balsam

Horsefly

OysterSnail Scallop

Rat

ElkDeer

BearSnakeChameleon Newt

Frog

Crab

Ge

ne

rati

on

Tim

e


• Age structure

– Determined by the numbers of individuals

in a different age group

– Cohort: group of individuals of the same

age

– Fecundity: number of offspring produced in

a standard time

– Mortality: death rate in a standard time

• Age structure has a critical influence on a

population’s growth rate16

17

Life tables show probability of survival and

reproduction through a cohort’s life

18


• Survivorship

– Percent of an original population that

survives to a given age

• Survivorship curve

– Express some aspects of age distribution Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

0Percent of Maximum Life Span

100755025

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Hydra (type II)

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Life History

• Natural selection favors traits that

maximize the number of surviving

offspring left in the next generation by

an individual organism

– 2 factors affect this quantity

• How long an individual lives

• How many young it produces each

year

19

• Life history

– Complete life cycle of an organism

• Trade-off: limited resources vs increased reproduction

20


5

2

1

Adult Mortality Rate per Year

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• Collared flycatchers (Ficedula albicollis)

– Experiment demonstrates the trade-off

between current reproductive effort and

future reproductive success

– Cost of reproductionCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

0–1–2

7

6

5

+2+1

Change in Clutch Size

Clu

tch

Siz

e F

ollo

win

g Y

ea

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a: © Christian Kerihuel

Life History

• In terms of natural selection, the number of

offspring produced is not as important as how

many of those offspring themselves survive to

reproduce

• Balance between number of offspring and

size of offspring– Larger offspring have a greater chance of survival

– Producing many small offspring may result in very low survival rates

22

23

Life History

Relationship between

clutch size and offspring

size

Variation in size

of baby side-

blotched lizards


80 2 4 6 141210

Clutch Size

17.5

18.0

18.5

19.0

19.5

Nes

tlin

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ize

(g

)

Life History

• Age at first reproduction correlates with

life span

– Long-lived species delay reproduction

• Advantage: juveniles gain

experience before high cost of

reproduction

– Short-lived species reproduce early

• Time is important; delay may mean

no offspring24

Environmental Limits to

Population Growth

• Populations often remain the same size

regardless of the number of offspring

born

• Exponential growth model applies to

populations with no growth limits

• Biotic potential – ability of a population

to grow in ideal conditions

25

• The biotic potential of any population is

exponential, even when the rate of increase

remains constant

– Result of unchecked exponential growth is

a population explosion

• All populations eventually reach some limit

imposed by a shortage

• Carrying capacity: symbolized by K, is the

maximum number of individuals that the

environment can support

26


Population Growth

• Logistic growth model: applies to populations as they reach K

• If you plot N versus t, you obtain a sigmoidal

growth curve

27


Population Growth

28

Red line illustrates the exponential growth model;

blue line illustrates the logistic growth model


0 5 10

Number of Generations (t)

Po

pu

lati

on

Siz

e (

N)

15

1250

1000

750

= 1.0 N

500

250

0

= 1.0 N

Carrying

capacity

1000 – N

1000

dN

dt

dN

dt

• As N approaches K, the rate of population growth

begins to slow

• If N = K the population growth rate is zero

– If the population size exceeds K, the population

size will decline until it reaches K 29


N = K

Above K

Population Size (N)

Below K Carrying

Capacity (K)

Positive

Growth

Rate

0

Negative

Growth

RatePo

pu

lati

on

Gro

wth

Ra

te (

dN

/dt)

30

Many populations exhibit logistic growth


1915 1925 1935 1945

a. b.

200 10 30 5040

10

8

6

4

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0

Nu

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Cla

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) 500

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200

100

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Nu

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Bre

ed

ing

Ma

le

Fu

r S

ea

ls (

tho

us

an

ds

)

Time (years) Time (days)

Factors That Regulate Populations

• Density-dependent

– Factors that affect the population and

depend on population size

• Density-independent

– Other factors, such as natural

disasters, affect populations

regardless of size

31

32


Density-dependent effects

result in negative feedback


Hig

hL

ow

Hig

hL

ow

Hig

hL

ow

Affecting Birth and Death Rates

Population Density

Affecting Birth Rates

Population Density

Affecting Death Rates

Population Density

Density-

dependent

death rate

Density-

dependent

birth rate

Equilibrium

population

density

Density-

dependent

death rate

Density-

independent

birth rate

Equilibrium

population

density

Density-

dependent

birth rate Density-

independent

death rate

Equilibrium

population

density

33

Density dependence in the song sparrow

on Mandarte island


1.0

2.0

3.0

4.0

5.0

0.4

0.5

0.6

0.7

0.8

0.9

140

Number of Breeding Adults

120100806040200

Nu

mb

er

of

Yo

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er

Fe

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le

Ju

ve

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Mo

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• Density-independent effects

– Rate of growth of a population at any instant is limited by something unrelated to the size of the population

– External environment aspects: cold winters, droughts, storms, volcanic eruptions

– Populations display erratic growth patterns because of these events

34


• North American snowshoe hare has a

10-year cycle

• Population numbers fall 10-fold to 30-

fold in a cycle, and 100-fold changes

can occur

• Two factors generate this cycle:

– Food plants

– Predators

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36


Linked population cycles of the snowshoe

hare and the Canada lynx

C. Krebs 1992: set up experimental plots to

determine if overharvesting of plants by

hares or increase lynx population cause

oscillations in populations

37


0

Nu

mb

er

of

Pe

lts

(in

th

ou

sa

nd

s)

160

120

80

40

1845 1855 1865 1875

Year

1885 1895 1905 1915 1925 1935

Snowshoe hare

Lynx


• Resource availability affects life history adaptations

• When resources are limited, the cost of reproduction is high

– Selection will favor individuals that can compete and utilize resources efficiently

– Can lower reproductive rates

– K-selected populations: adapted to thrive when population is near its carrying capacity 38


• Populations far below carrying capacity, resources abundant

– Costs of reproduction are low

– r-selected populations: selection favors individuals with the highest reproductive rates

• Most natural populations show life history adaptations that exist along a continuum of r- and K-selected traits

39

Human Population Growth

• K-selected life history traits

– Small brood size

– Late reproduction

– High degree of parental care

• Changes since the 1700s allowed humans to escape logistic growth

• Human populations have grown exponentially

– Birth rate has remained unchanged

– Death rate has fallen dramatically

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42

History of human

population size


Projected population

growth in 2050


2

1

3

4

5

6

7

0

Bil

lio

ns

of

Pe

op

le

Significant advances

in public health

Industrial

Revolution

20001000

Year

4000

B.C.

3000

B.C.

2000

B.C.

1000

B.C.

Bubonic plague

“Black Death”


0

907Po

pu

lati

on

(in

mil

lio

ns

)

200

400

600

800

1000

1200

1400

1600

1800

2000 1931

5000

60005350

7000 6721

527

685

375

871

767

516

4833

South

America

North

AmericaEuropeAustralasiaAsiaAfrica

2005

2050

• Population Pyramid

– Bar graph displaying the number of people

in each age category

– Kenya’s population could double in less

than 35 years, whereas Sweden’s will

remain stable

43

44

Ag

e

039 6 3 6 9048 4 8

Percent of Total Population

18151218 1215

100+

95–99

90–94

85–89

80–84

75–79

70–74

65–69

60–64

55–59

50–54

45–49

40–44

35–39

30–34

25–29

20–24

15–19

10–14

5–9

0–4

Sweden Kenya

male

female


• Earth’s rapidly growing human population

constitutes perhaps the greatest challenge to

the future of the biosphere

• Uneven distribution among countries

• Increasing gap between rich and poor

• The world ecosystem is already under stress

• What is K for the human population?

45

47Distribution of population growth

Human Population GrowthCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1

2

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0

Wo

rld

Po

pu

lati

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in

Billio

ns

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10

World total

Developing countries

low fertility

Developed countries

20502000Time

19501900


• World population growth rate is declining

– High of 2.0% in 1965–1970

– 1.2% in 2008

– Still an increase of 78 million people per year

• Attributed to increased family planning

efforts and the increased economic

power and social status of women

48


• Consumption in the developed world further depletes resources

– Wealthiest 20% of the world’s population accounts for 86% consumption of resources and produces 53% of CO2 emissions

– Poorest countries: 20% is responsible for 1.3% consumption and 3% CO2emissions

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50

Ecological Footprint: amount of productive land required to support an individual at the standard of living of a particular population through the course of his/her life

Human Population GrowthCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2

0

4

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2.22.23.2

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Ecology of Individuals and Populations · 2020. 1. 26. · Human Population Growth •K-selected...

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Transcript of Ecology of Individuals and Populations · 2020. 1. 26. · Human Population Growth •K-selected...